Add iSCSI APIs (#99)

* Adding the iSCSI APIs

1. Currently has a very limited support for Multipath
2. Does not contain node level APIs to set reverse
   CHAP or node IQN
3. Tests format a disk, so special flag is used to
   enable the iSCSI tests. Take care to use
   disposable clean VMs for tests.

Change-Id: I0fe8431fed00715883ad0431671ec6a060718e0e

* Adding newly added vendor files

Change-Id: Ib669ed4aafad4a7ce6fa4821998e24264072c049

* Removing iSCSI tests from integration tests

I've tried the test on a clean GCP Windows 2016/2019
VM and this works.
This might be related to the Server Target feature
install on the github workflow environment.
Might be worth fixing with the other disabled
integration tests.

Change-Id: If76902118f1a2887caf5c554d339ad1dc13f04a8

* Fixing code review issues

1. Fixing errors in proto comments
2. Adding missing comments for AuthenticationType enum
3. Renaming DiskIds to DiskIDs to better conform to other apis
4. Documenting lack of initiator selection features in AddTargetPortal
5. Improving multipath related documentation

Change-Id: Ic9ec4387a140f522fa2e3a3ad781a439bc2cb918

* Remove multipath option from API

This was decided as currently we don't have a way of specifying
different initiators. Effectively making multipath very limited
in usage, as well as probably confusing

Change-Id: I0cd9b7fa7cdb309dbc29ab1a5a5c64909a429f1e

README.md

@@ -99,6 +99,8 @@ spec:
               mountPath: \\.\pipe\csi-proxy-volume-v1alpha1
             - name: csi-proxy-filesystem-pipe
               mountPath: \\.\pipe\csi-proxy-filesystem-v1alpha1
+            - name: csi-proxy-iscsi-pipe
+              mountPath: \\.\pipe\csi-proxy-iscsi-v1alpha1
       volumes:
         - name: csi-proxy-disk-pipe
           hostPath:
@@ -112,6 +114,10 @@ spec:
           hostPath:
             path: \\.\pipe\csi-proxy-filesystem-v1alpha1
             type: ""
+        - name: csi-proxy-iscsi-pipe
+          hostPath:
+            path: \\.\pipe\csi-proxy-iscsi-v1alpha1
+            type: ""
         - name: registration-dir
           hostPath:
             path: C:\var\lib\kubelet\plugins_registry\