Enable path expansion in GCE modules

This is basically a replay of #16064 from `gce.py` to other pertinent
`gce_*.py` files. It enables expansions of paths in `gce.ini` like
`~/.project.json`

lib/ansible/modules/cloud/google/gce_eip.py

@@ -179,8 +179,8 @@ def main():
         region=dict(required=True),
         service_account_email=dict(),
         service_account_permissions=dict(type='list'),
-        pem_file=dict(),
-        credentials_file=dict(),
+        pem_file=dict(type='path'),
+        credentials_file=dict(type='path'),
         project_id=dict(), ), )
 
     if not HAS_PYTHON26:

lib/ansible/modules/cloud/google/gce_lb.py

@@ -193,8 +193,8 @@ def main():
             members = dict(type='list'),
             state = dict(default='present'),
             service_account_email = dict(),
-            pem_file = dict(),
-            credentials_file = dict(),
+            pem_file = dict(type='path'),
+            credentials_file = dict(type='path'),
             project_id = dict(),
         )
     )

lib/ansible/modules/cloud/google/gce_mig.py

@@ -721,8 +721,8 @@ def main():
         named_ports=dict(type='list', default=None),
         service_account_email=dict(),
         service_account_permissions=dict(type='list'),
-        pem_file=dict(),
-        credentials_file=dict(),
+        pem_file=dict(type='path'),
+        credentials_file=dict(type='path'),
         project_id=dict(), ), )
 
     if not HAS_PYTHON26:

lib/ansible/modules/cloud/google/gce_net.py

@@ -329,8 +329,8 @@ def main():
             target_tags = dict(type='list'),
             state = dict(default='present'),
             service_account_email = dict(),
-            pem_file = dict(),
-            credentials_file = dict(),
+            pem_file = dict(type='path'),
+            credentials_file = dict(type='path'),
             project_id = dict(),
             mode = dict(default='legacy', choices=['legacy', 'auto', 'custom']),
             subnet_name = dict(),

lib/ansible/modules/cloud/google/gce_pd.py

@@ -176,8 +176,8 @@ def main():
             state = dict(default='present'),
             zone = dict(default='us-central1-b'),
             service_account_email = dict(),
-            pem_file = dict(),
-            credentials_file = dict(),
+            pem_file = dict(type='path'),
+            credentials_file = dict(type='path'),
             project_id = dict(),
         )
     )