Fix gae.py's detection of current active credentials.

Fix gae.py's detection of current active credentials.

There are two problems:
1. Looks like gcloud is not using ~/.config/cloud/credentials anymore. We now
   use public API to check for current active account instead.
2. Looks like appcfg.py is not aware of gcloud's credentials anymore, so we need
   to reintroduce appcfg-specific login command again. We call it appcfg_login.
   This will go away soon-ish once we switch to gcloud as the only supported
   mode of operation.

R=nodir@chromium.org, maruel@chromium.org
BUG=747588
Review-Url: https://codereview.chromium.org/2987613002
Committed: https://github.com/luci/luci-py/commit/8b90cdd97f8f088bcba2fa376ce49d9863b48902

[Vadim Sh., 2017-07-21 23:32:40]

PTAL

"hacks, hacks everywhere"
http://3dn6i8277y3e2terx93zyfk5.wpengine.netdna-cdn.com/wp-content/uploads/20...

[nodir, 2017-07-21 23:39:08]

lgtm

[Vadim Sh., 2017-07-21 23:41:08]

The CQ bit was checked by vadimsh@chromium.org

[commit-bot: I haz the power, 2017-07-21 23:41:15]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-07-21 23:45:07]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1500680468891540,
"parent_rev": "421927b9bb0fa68f8b36394c5b12dc6aec3c0e2f", "commit_rev":
"8b90cdd97f8f088bcba2fa376ce49d9863b48902"}

[commit-bot: I haz the power, 2017-07-21 23:45:10]

Description was changed from

==========
Fix gae.py's detection of current active credentials.

There are two problems:
1. Looks like gcloud is not using ~/.config/cloud/credentials anymore. We now
   use public API to check for current active account instead.
2. Looks like appcfg.py is not aware of gcloud's credentials anymore, so we need
   to reintroduce appcfg-specific login command again. We call it appcfg_login.
   This will go away soon-ish once we switch to gcloud as the only supported
   mode of operation.

R=nodir@chromium.org, maruel@chromium.org
BUG=747588
==========

to

==========
Fix gae.py's detection of current active credentials.

There are two problems:
1. Looks like gcloud is not using ~/.config/cloud/credentials anymore. We now
   use public API to check for current active account instead.
2. Looks like appcfg.py is not aware of gcloud's credentials anymore, so we need
   to reintroduce appcfg-specific login command again. We call it appcfg_login.
   This will go away soon-ish once we switch to gcloud as the only supported
   mode of operation.

R=nodir@chromium.org, maruel@chromium.org
BUG=747588

Review-Url: https://codereview.chromium.org/2987613002
Committed:
https://github.com/luci/luci-py/commit/8b90cdd97f8f088bcba2fa376ce49d9863b48902
==========

[commit-bot: I haz the power, 2017-07-21 23:45:11]

Committed patchset #2 (id:20001) as
https://github.com/luci/luci-py/commit/8b90cdd97f8f088bcba2fa376ce49d9863b48902