Declare bzr TERM=dumb to silence progress bars

In theory, one could set BZR_PROGRESS_BAR=none but it does not work in 1.14rc2

tests/bzr-definitions

@@ -2,6 +2,7 b''
 
 "$TESTDIR/hghave" bzr || exit 80
 
+export TERM=dumb
 echo '[extensions]' >> $HGRCPATH
 echo 'convert = ' >> $HGRCPATH
 echo 'hgext.graphlog = ' >> $HGRCPATH