[autotest] makes package-based install work with dash shell

The autotest package-based install fails on DUTs running the 'dash'
shell due to a non-POSIX-compliant pathname expansion pattern.
Changes the pattern to make it POSIX-compliant.

Reference: Section 2.13.1 in
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html

http://www.gnu.org/software/bash/manual/bashref.html#index-pathname-expansion

BUG=chrome-os-partner:40702
TEST=Running autotest with this patch on moblabs.

Change-Id: Id952e19c67aaa6d74eaa09e478201693c98dc95c
Reviewed-on: https://chromium-review.googlesource.com/284360
Trybot-Ready: Laurence Goodby <lgoodby@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Commit-Queue: Laurence Goodby <lgoodby@chromium.org>
Tested-by: Laurence Goodby <lgoodby@chromium.org>
diff --git a/server/autotest_unittest.py b/server/autotest_unittest.py
index ac5893d..247380a 100755
--- a/server/autotest_unittest.py
+++ b/server/autotest_unittest.py
@@ -158,7 +158,7 @@
             run_function=self.host.run, run_function_dargs=dict(timeout=600))
         pkg_dir = os.path.join('autodir', 'packages')
         cmd = ('cd autodir && ls | grep -v "^packages$"'
-               ' | xargs rm -rf && rm -rf .[^.]*')
+               ' | xargs rm -rf && rm -rf .[!.]*')
         self.host.run.expect_call(cmd)
         pkgmgr.install_pkg.expect_call('autotest', 'client', pkg_dir,
                                        'autodir', preserve_install_dir=True)