Change CM recovery install script filename [1/2]

This is part 1/2 to maintain backwards compatibility with CWM's
verify_root_and_recovery() function. CWM checks if install-recovery.sh
exists and has an executable flag set, then offers to disable the script
for the user. CM now controls this with the persist.sys.recovery_update
property which is configurable via settings, so we don't need to
double-check this.

This changes the name of the recovery install script to
install-cm-recovery.sh.

Change-Id: Ie08d428cfd092a1de10973ba5ffc326ccdb1a369
keys: avoid duplicating recovery keys

Setting PRODUCT_EXTRA_RECOVERY_KEYS duplicates the default key and
makes it so we can't set an extra key earlier in the build

Change-Id: I239d9994d9ad40b1779877ea2e89b55bd02e4c00