Build: Small workaround

  * Until the real problem is solved lets unmount partions prior to flash
  * Based on Vonnegut@XDA recommendation

Change-Id: If2ec54f5e273f1c92868672ed365f246ace54b70
Signed-off-by: Josue Rivera <prbassplayer@gmail.com>
Merge "Build: Small workaround" into lp5.0