Make scons build thread-safe (i.e., support -jNN)
- Avoid use of chdir=1 in Action() and/or Command()
- Prepend "cd $dir && " to relevant commands

Change-Id: I504cbaf61056cf05fa630b3aaab316a949d7797b
Merge "Make scons build thread-safe (i.e., support -jNN) - Avoid use of chdir=1 in Action() and/or Command() - Prepend "cd $dir && " to relevant commands"