frecovery: Improve adb usage
frecovery: Improve adb usage

* Use common '${adb}'
* 'wait-for-device' before reboot to bootloader

Change-Id: I83399d833e19dbb1c9570510e6a5bc35ddedda8f
Signed-off-by: Caio Oliveira <4db4e54f91055ffa8197b8408ec5b5470f9993b8@gmail.com>

AdrianDC/android_development_shell_tools,AdrianDC/android_development_shell_tools