dvc: don't include gssapi

If user needs it, he can install it by himself through pip.

https://github.com/iterative/dvc/pull/2424#issuecomment-523990535

https://github.com/iterative/dvc.org/pull/582

setup.py

@@ -75,7 +75,12 @@ gs = ["google-cloud-storage==1.13.0"]
 s3 = ["boto3==1.9.115"]
 azure = ["azure-storage-blob==2.1.0"]
 oss = ["oss2==2.6.1"]
-ssh = ["paramiko[gssapi]>=2.5.0"]
+ssh = ["paramiko>=2.5.0"]
+# gssapi should not be included in all_remotes, because it doesn't have wheels
+# for linux and mac, so it will fail to compile if user doesn't have all the
+# requirements, including kerberos itself. Once all the wheels are available,
+# we can start shipping it by default.
+ssh_gssapi = ["paramiko[gssapi]>=2.5.0"]
 hdfs = ["pyarrow==0.14.0"]
 all_remotes = gs + s3 + azure + ssh + oss
 
@@ -131,6 +136,7 @@ setup(
         "azure": azure,
         "oss": oss,
         "ssh": ssh,
+        "ssh_gssapi": ssh_gssapi,
         "hdfs": hdfs,
         # NOTE: https://github.com/inveniosoftware/troubleshooting/issues/1
         ":python_version=='2.7'": ["futures", "pathlib2"],