[cipd] Update CIPD client to 2.6.0.

It now fetches and installs packages in parallel. This has a side
effect that the order of unzipping of packages in a manifest is
non-deterministic and depends on when particular packages finish
downloading.

To be able to show progress of parallel operations there's also
a new terminal UI with progress bars. It activates when running
CIPD at `info` logging level (default) if the stderr is attached
to a terminal (i.e. not piping to a file or the recipe engine).

Two new env vars control the new behavior:
 * CIPD_PARALLEL_DOWNLOADS: set to 0 to completely disable
   parallelism and restore pre 2.6.0 behavior. Set to 1 to fetch
   and unzip packages in paralle, but fetch at most one package
   at once. Default is 4.
 * CIPD_SIMPLE_TERMINAL_UI: set to 1 to use log-based UI instead
   of progress bars.

R=iannucci@chromium.org
BUG=1217435

Change-Id: I16815dbc397137fbb8ef09e09d0a04c77660c0c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2993750Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>

cipd_client_version

-git_revision:6484b93c6b0dfc5f2c425e8abc1e3737850851e7
+git_revision:4511c670f851c56473a7370c10c199cdad4dfc3c

cipd_client_version.digests

 # This file was generated by
 #
 #  cipd selfupdate-roll -version-file cipd_client_version \
-#      -version git_revision:6484b93c6b0dfc5f2c425e8abc1e3737850851e7
+#      -version git_revision:4511c670f851c56473a7370c10c199cdad4dfc3c
 #
 # Do not modify manually. All changes will be overwritten.
 # Use 'cipd selfupdate-roll ...' to modify.
 
-aix-ppc64       sha256  f7bc16a7f16af429bca943a5181bb2a0f2d1fb264a20ab0cc4df59dce506be90
-linux-386       sha256  8a8612b43aada6e05e5b4782c80e9d2a1ee710b419c5065a496bc25b73428e7b
-linux-amd64     sha256  73096e0da6a83054c74ed0a7df44c0160664d13573e897e37592b2379b7f7348
-linux-arm64     sha256  0b628e7918eb2661fc83b475fc2e5e9d8023b0b2406d4895f35940b0ea8d030d
-linux-armv6l    sha256  2ea7781f36a8abb8de6e0ec677cf44127ff4724a292861f949df3f326542da97
-linux-mips64    sha256  5c751c58ec7790a4c262fd6ce569b82b8e0565881514a802d61a72a408b5f8bb
-linux-mips64le  sha256  249e20ae499186e4c002ac78f5f9b95962b0c2f3a579756d2b3462ff2902b670
-linux-mipsle    sha256  db6b8bf8f2269581c2b2303aa850e1282540bbb8599e9c874e9c179712e4c174
-linux-ppc64     sha256  4bb77c5da747a7bbc72807092e0ebd2571465491c49f530a5f2ad55b23bd5141
-linux-ppc64le   sha256  4b232bbf1da18ed8cae4a37a44509c4c068c4da19963b18c36e04a68fc0c60a1
-linux-s390x     sha256  f106ad74ed0070d949ddca736a00d4010130089260b62f7b2777e007b3fda68a
-mac-amd64       sha256  1c8ed715d1f0e18a52b29aa7b4eda8b2d0b4bbfbf727e6e9cbc4609d0e73fe09
-mac-arm64       sha256  f436a1d69dfce70b929f5ed36eadf12f441f2bfbeee8cd58475852317010a55a
-windows-386     sha256  c24e885a4f37d01e03a7dbff3aeab1d7dba4f8cb6aa1899c9c13151d1a6f5f81
-windows-amd64   sha256  bf564d627fd35b30c7d57696f840d75e63e8f17119576f58bb45311fce987e94
+aix-ppc64       sha256  0696f6979153a326f5269ac24cc03a834de8472fc35d467efe13618d30186332
+linux-386       sha256  0299c0a3b1a86bccfb1ef974b981827649a64c42406205126e789b7cba466839
+linux-amd64     sha256  d2ef210cdcc2df1f3d0c74c5918999088426490ed000f009ebd7fdaec1f77222
+linux-arm64     sha256  98ccdf942ecee4744aa6469e4093e025983d005f9a22e34c0d35d70accc77351
+linux-armv6l    sha256  b74057db288278ccaa67bb444b5e6e84dbef0912636ca06fadf10f3f98c04ebe
+linux-mips64    sha256  1850c72d660bf1096b827aad422927fedc2f61428ff89c7f50ff05340bc226e1
+linux-mips64le  sha256  ceb9571d9fbcdd70d3744e96f69c55c53b2feec60b6326d59141a2a308acc87c
+linux-mipsle    sha256  07d1ecba6e9b33fdf7b5c31e82768579ee8633caeb439a566e3d8bdda589b575
+linux-ppc64     sha256  cffb1bd349b6eb53389d3318b88c73cf73fd8b56897f53a0bad455fbeacf501b
+linux-ppc64le   sha256  e021b4f6442a2b88018f008c6969776b4cc2c592de9107c07a43f182ef51e169
+linux-s390x     sha256  e91fe9df5b17bbefbe098a661581e3c61b940f5ec0303320d929ab86a6c4645c
+mac-amd64       sha256  d4e065720036cd381810e8503fa4c6cc45d69c19179ab35ba4eb0969a8580341
+mac-arm64       sha256  e4f78c9d58ab982419abcb5153f69050eeab7d28cac55ce8e8a9e12f822c2055
+windows-386     sha256  b761be1d35aa0d3b63a1aeaaf9a4952447fa7ea681e84dce603980a176092f17
+windows-amd64   sha256  53baa50b2f7cdcaa0e15510a2fd0debc0297db7914d848e209779ae74aaa3931