Update GCE scripts to create and mount a 2TB persistent disk to skia-testing

BUG=skia:3147

Review URL: https://codereview.chromium.org/741053002
Update setup scripts to log into the new mounted 2TB persistent disk on skia-testing-b.
Also up the AppLogLevel threshold in logserver to 1GB.

BUG=skia:3147

Review URL: https://codereview.chromium.org/743163002
Put the logserver.state file in the 2TB mounted disk

BUG=skia:3147
TBR=jcgregorio

Review URL: https://codereview.chromium.org/742113002
Specify --dir to logserver_init

BUG=skia:3147
TBR=jcgregorio

Review URL: https://codereview.chromium.org/743193002
Use time's Since() function.

According to golang.org/pkg/time/#Since doc, it is a shorthand for:
time.Now().Sub(t)

BUG=None
R=borenet@google.com

Review URL: https://codereview.chromium.org/742833004
Add auto-refresh to Alert Server

BUG=skia:

Review URL: https://codereview.chromium.org/741023002
Another fix to perf_setup.sh

BUG=skia:3131
TBR=jcgregorio

Review URL: https://codereview.chromium.org/746473002
bug_chomper: Fix 'go get -u' warning.

When running 'go get -u skia.googlesource.com/buildbot.git/...

You would get:
imports issue_tracker: unrecognized import path "issue_tracker"

BUG=None
TEST=see above
R=borenet@google.com

Review URL: https://codereview.chromium.org/737113002