adb: added support for adb pull -a to preserve time stamps and mode

Added -a flag to adb pull that preserves time and mode.  Mode is
subjected to umask for security.  We only receive modification
time from adb server, so creation time will be set to the modification
time as well.

Change-Id: I37c0b94741ed464f19025d25dea3ff2f6ac43e7f
Signed-off-by: Lajos Molnar <lajos@google.com>