adb: add -Tt options to `adb shell`.

Adds -T (no PTY) and -t (force PTY) options to `adb shell` to mimic
ssh options. Small cleanup to send an entire FeatureSet to the adb
client at once to avoid multiple round-trips when querying multiple
features.

Known issue: humans using `adb shell -T` to start a non-PTY interactive
session may experience problems since neither side will have PTY
features like echoing or newline translation. This is probably OK for
now as the -Tt options are primarily useful for scripting.

Bug: http://b/23825231
Change-Id: I4d0df300db0abd1f7410bab59dd4d5b991babda7