Squashed 'external/devlib/' changes from 528d3d4e0..0e0417c6b

0e0417c6b target: Fix undefined function
e979bafb5 target: Speedup Target.write_value()
0c1878786 Target.execute(): Add .returncode and .output exception attributes
ff57e785f exception: Deal with missing _message attribute
f1c8ca1a6 utils.android: Separate stdout and stderr by newline
b719808ef target: Add Target.pull(via_temp=False) parameter
477e82c44 target: Open the possiblity for optimizing multi-source push/pulls
173df18f2 target: Factorize push/pull path resolution
79be8bc5a ssh: Memoize the SshConnection._get_sftp()
55d914bf9 target: Fix typo in Target._prepare_xfer

git-subtree-dir: external/devlib
git-subtree-split: 0e0417c6b32c63501ef3063eb128a34535b359b4