IMPALA-4570: shell tarball breaks with certain setuptools versions

The bug was in the third-party pkg_resources.py script. The version
check was broken because it matches any version with a "0.7" substring
instead of just versions starting with 0.7.

This is a known bug. setuptools even re-released 20.7.0 as version
20.8.0 to avoid it:
e5822f0d5b

Testing:
I was unable to reproduce this locally, but I think the fix is clear-cut
enough that this is ok.

Change-Id: I0565c0e6c1be7d82c3f35d2545ba044a684bb075
Reviewed-on: http://gerrit.cloudera.org:8080/5314
Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com>
Tested-by: Impala Public Jenkins

shell/pkg_resources.py

@@ -2292,7 +2292,7 @@ class Distribution(object):
                 version = self.version
             except ValueError:
                 version = ''
-            if '0.7' in version:
+            if version.startswith('0.7'):
                 raise ValueError(
                     "A 0.7-series setuptools cannot be installed "
                     "with distribute. Found one at %s" % str(self.location))
@@ -2593,7 +2593,7 @@ def _override_setuptools(req):
             return True
         for comparator, version in req.specs:
             if comparator in ['==', '>=', '>']:
-                if '0.7' in version:
+                if version.startswith('0.7'):
                     # We want some setuptools not from the 0.6 series.
                     return False
         return True