[swarming] Roll luci-go/isolate.

Ports https://codereview.chromium.org/1671753002

It brings auth support (so developers can use 'isolate' if
they really want to) and adds *.pyc to default isolate
blacklist.

TBR=maruel@chromium.org,  vadimsh@chromium.org, stip@chromium.org
BUG=584073
LOG=n

Review URL: https://codereview.chromium.org/1677453002

Cr-Commit-Position: refs/heads/master@{#33763}

tools/luci-go/linux64/isolate.sha1

-19c8b40bf2f18f58e748c42e8da71d558805014d
+cf7c1fac12790056ac393774827a5720c7590bac

tools/luci-go/mac64/isolate.sha1

-fbc5e25238075b10f70eab6072dbeb9739e4e5ce
+4678a9332ef5a7b90b184763afee1c100981f710

tools/luci-go/win64/isolate.exe.sha1

-7a6fd72a5d7e9880546675088a6f2e94e09c5249
+98457ff4fc79d05661fea53d2b3aff70fac90022