Backwards compatible imports for exceptions that are now in pytest-sh…

…ell-utilities

Fixes saltstack#108

Signed-off-by: Pedro Algarvio <palgarvio@vmware.com>

changelog/108.bugfix.rst

@@ -0,0 +1 @@
+Provide backwards compatibility imports for the old factory exceptions, now in pytest-shell-utilities

src/saltfactories/exceptions.py

@@ -1,6 +1,30 @@
 """
 PyTest Salt Factories related exceptions.
 """
+import sys
+
+if sys.version_info >= (3, 7):
+
+    def __getattr__(name):
+        if name in ("FactoryTimeout", "FactoryNotStarted"):
+            import pytestshellutils.exceptions
+            from saltfactories.utils import warn_until
+
+            warn_until(
+                "2.0.0",
+                "The '{}' exception is now in 'pytestshellutils.exceptions' and importing it "
+                "from 'saltfactories.exceptions' is deprecated and will cease to work after "
+                "pytest-salt-factories {{version}}.".format(name),
+            )
+            return getattr(pytestshellutils.exceptions, name)
+        else:
+            raise AttributeError("module '{}' has no '{}' attribute".format(__name__, name))
+
+else:
+    # pylint: disable=unused-import
+    from pytestshellutils.exceptions import FactoryNotStarted, FactoryTimeout  # noqa: F401
+
+    # pylint: enable=unused-import
 
 
 class SaltFactoriesException(Exception):