floss: Add timeout for git clone

Git clone operation is timing out in CI so add a 10-minute timeout to
this command. The default timeout can be changed via the --clone-timeout
option in build.py.

Bug: 336365190
Test: Build in container with different timeouts.
Test: m Bluetooth
Flag: EXEMPT only affects floss linux build

Change-Id: Ia93c1c8fd85f348521020822cecba32688c3cb66