Make pip InstallationError import more robust

The way the version check was implemented fails on ancient pip versions
that do not provide pip.__version__ yet.

We will therefore simply try to import InstallationError and fall back
to ValueError if it has not been defined in the installed pip version.

salt/states/pip_state.py

@@ -49,11 +49,9 @@ if HAS_PIP is True:
         if 'pip' in sys.modules:
             del sys.modules['pip']
 
-    ver = pip.__version__.split('.')
-    pip_ver = tuple([int(x) for x in ver if x.isdigit()])
-    if pip_ver >= (8, 0, 0):
+    try:
         from pip.exceptions import InstallationError
-    else:
+    except ImportError:
         InstallationError = ValueError
 
 # pylint: enable=import-error