Begin moving code from adb to libadb.

Much of adb is duplicated in bootable/recovery/minadb and fastboot.
Changes made to adb rarely get ported to the other two, so the trees
have diverged a bit. We'd like to stop this because it is a
maintenance nightmare, but the divergence makes this difficult to do
all at once. For now, we will start small by moving common files into
a static library. Hopefully some day we can get enough of adb in here
that we no longer need minadb.

Bug: 17626262
Change-Id: Ic8d5653bfcc0fec4e1acbece124402355084b864