daemon: Set TERM=dumb inside the daemon.

Since commit 977edb3185fe8f we have been passing TERM from the
library into the appliance (for the benefit of virt-rescue).
However this changes the output of parted, which I would argue
is a bug in parted:

 TERM=xterm /sbin/parted -m -- /dev/sda unit b print 2>&1 | hexdump -C
 00000000  1b 5b 3f 31 30 33 34 68  42 59 54 3b 0a 2f 64 65  |.[?1034hBYT;./de|

Notice the escape-sequence junk before the official "BYT;"
header.

By setting TERM=dumb we avoid this.