Signing key can be submitted by putting key at a fixed location
(key/privatekey.pem) or by putting the key location in environment
variable PRIVATE_KEY_PATH. The script checks for either of those
possibilities.
ovftool command was incorrectly using the PRIVATE_KEY_PATH variable
even when the key file was dropped in the prescribed location.
Set the serial console speed to 115200 in all build scripts, as is the
standard for current boards. This avoids an annoyance for users of the
livecd, and makes the defaults in build scripts in tools/ and scripts/
consistent.
