Fix how install_worker on CDROM and output redirect.

Major bugs:
1) We were not properly passing the arguments down when exec'ing outselves
because $@ is lost unless passed down into the function.
2) We were clobbering fd 3 and 4 when running against logger(1) causing
us to lose our django error output.

While here:
1) fix how usage() is handled, save a special fd for that
and have usage spit to that handle.
2) use warn() instead of echo when logger/mkfifo isn't available.
3) rename logfiles to "$TMPDIR/install_worker.foo"
4) when using logger(1) ALSO log to $FIFO_DIR/install.log for
consistency.
Remove the dirty bit, it was causing confusion for users.

(cherry picked from commit be5302c48cffce72e373fb151bd97d35fea6ce56)
Fix issues in 738f085e a298b3be.

create_iso.sh generated the 0005.verify_media_size.sh script
and in the process would write the current value (during build)
of IMG_SIZE hardwired into the script.

In addition most of the other variables were escaped with \$, however
now that the file is being copied the variables no longer need to
be escaped.