Add an opt-out environment variable for build completion notifications

add export VANIR_DISABLE_BUILD_COMPLETION_NOTIFICATIONS=0 to your .bashrc to disable these popups

Change-Id: Ic7e6737dbee64497c22867f397f5300fa8b28bfa
Revert "Revert "Revert "Don't wipe cache and dalvik"""

Periodically, the ROM will come up in a state where an important class can't be found in the dalvik-cache.
The issue is remedied by wiping dalvik-cache to fix it.

The gains of not having this happen justify never having the rare non-invalidated-dalvik-cache flash.

This reverts commit 1da7bb7f2aff8caa7a741fb0178653b64e58b8ab.