Bug 996491: Show warning when using snapshot and near disk quota

When the gear user's disk usage is >= 90% of quota, display a warning when
snapshotting or restoring (as these operations can fail in unexpected ways
when disk writes fail).
Fix bug 999013: always remove unprocessed env/*.erb files from cartridge dir during compatible upgrade
Fix bug 999189: gear upgrade extension is a no-op if release version doesn't match supplied version
Merge pull request #3427 from ironcladlou/bz/996491

Merged by openshift-bot
Merge pull request #3440 from pmorie/bugs/999013

Merged by openshift-bot
Merge pull request #3449 from pmorie/bugs/999189

Merged by openshift-bot