test-convert-cvs: make test compatible with chg

The test uses the 'print' method instead of writing to stdout using
'ui.write' which leads to incompatibility with chg. This commit modifies the
test to use the 'ui' object instead which fixes the problem.

Test Plan:
Ran the test 'test-convert-cvs.t' with and without '--chg' option.

Differential Revision: https://phab.mercurial-scm.org/D923

tests/test-convert-cvs.t

@@ -12,10 +12,10 b''
   $ echo "convert = " >> $HGRCPATH
   $ cat > cvshooks.py <<EOF
   > def cvslog(ui,repo,hooktype,log):
-  >     print("%s hook: %d entries"%(hooktype,len(log)))
+  >     ui.write('%s hook: %d entries\n' % (hooktype,len(log)))
   > 
   > def cvschangesets(ui,repo,hooktype,changesets):
-  >     print("%s hook: %d changesets"%(hooktype,len(changesets)))
+  >     ui.write('%s hook: %d changesets\n' % (hooktype,len(changesets)))
   > EOF
   $ hookpath=`pwd`
   $ cat <<EOF >> $HGRCPATH