PYCBC-1711: Don't set bucketType, replicaIndex, flushEnabled when creating bucket unless set by user

Motivation
==========
We should only set bucket settings that the user has explicitly set. In this case, the SDK defaults are aligned with the server defaults, so removing them does not change default behavior.

Changes
=======
Don't set bucketType, replicaIndex, flushEnabled in create/update bucket requests unless the user has set them.

Results
=======
* All tests pass.
* FIT tests (BucketManagerTest) now only fail due to the presence of replicaNumber which is tracked by PYCBC-1712.

Change-Id: I16fb71542215290f8b55151710522ee2433b8a83
Reviewed-on: https://review.couchbase.org/c/couchbase-python-client/+/234247
Reviewed-by: Jared Casey <jared.casey@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>

Author: DemetrisChr

couchbase/management/logic/buckets_logic.py

@@ -347,8 +347,7 @@ class BucketSettings(dict):
     mapping = BidirectionalMapping([
         BidirectionalTransform("flush_enabled",
                                ParamTransform("flushEnabled", Identity(bool)),
-                               ParamTransform("flushEnabled", Identity(bool)),
-                               default=False),
+                               ParamTransform("flushEnabled", Identity(bool))),
         BidirectionalTransform("num_replicas",
                                ParamTransform("numReplicas", Identity(int)),
                                ParamTransform("numReplicas", Identity(int)),
@@ -358,14 +357,12 @@ class BucketSettings(dict):
                                ParamTransform("ramQuotaMB", Identity(int))),
         BidirectionalTransform("replica_index",
                                ParamTransform("replicaIndex", Identity(bool)),
-                               ParamTransform("replicaIndex", Identity(bool)),
-                               default=False),
+                               ParamTransform("replicaIndex", Identity(bool))),
         BidirectionalTransform("bucket_type",
                                ParamTransform(
                                    "bucketType", EnumToStr(BucketType)),
                                ParamTransform(
-                                   "bucketType", StrToEnum(BucketType)),
-                               default=BucketType.COUCHBASE),
+                                   "bucketType", StrToEnum(BucketType))),
         BidirectionalTransform("max_ttl",
                                ParamTransform("maxTTL", Identity(int)),
                                ParamTransform("maxTTL", Identity(int))),
@@ -419,7 +416,7 @@ class BucketSettings(dict):
     @overload
     def __init__(self,
                  name=None,  # type: str
-                 flush_enabled=False,  # type: bool
+                 flush_enabled=None,  # type: bool
                  ram_quota_mb=None,  # type: int
                  num_replicas=0,  # type: int
                  replica_index=None,  # type: bool
@@ -475,7 +472,7 @@ def replica_index(self):
     def bucket_type(self):
         # type: (...) -> BucketType
         """BucketType {couchbase (sent on wire as membase), memcached, ephemeral}
-        The type of the bucket. Default to couchbase."""
+        The type of the bucket. Defaults to the server default (couchbase)."""
         return self.get('bucket_type')
 
     @property