config: Fix some synchronization issues

The file read errors could interleave randomly since there was no
synchronization in place really. Changed the code to use channels.

Also had to extend the log package a bit for the new logging needs.

Change-Id: f65def0942
Story-Id: 78913390
Update review with single commit only.

Currently we only support last comit on HEAD.

Change-Id: 3a1a283a26
Story-Id: 78982718
Make sure gitflow config file or branch is not mentioned anywhere.

Abstract out the names.

Change-Id: b35364c3cd
Story-Id: 78913658
Refactoring.

 * Added `panic` function that yells and exits.
 * Minor improvements (less polluted console output etc).

Change-Id: eef659d552
Story-Id: 78913658
Ignore unestimated stories. 

 * I’ve added a `—ignore-unestimated` flag to `pivotal_tools` so that unestimated features are not listed.

Change-Id: 1592804b3c
Story-Id: 78913658
Better handling of existing story branches.

If there’s just one story branch, checkout it.

Change-Id: 142ded5922
Story-Id: 78913658
Install new pivotal shell module too.

Change-Id: ad32122602
Story-Id: 78913658
Fixed invalid `panic` output when no story-id is found.

Change-Id: 7385f04aa9
wip

Change-Id: 6d763ac559
Story-Id: 78913390