envsetup: Wait for device in installboot/installrecovery

 * Useful when you're racing against a bug that causes a kernel panic
   shortly after USB turns on :(

Change-Id: I2a503e4b195e632ed5b67a77b942e80c47d0ff45
Merge pull request #3 from CyanogenMod/cm-10.2

envsetup: Wait for device in installboot/installrecovery