Mongo go driver beta integration (#1042)

* Changed mongo.go to use new driver

* Modified mongo cataloger

* More new driver related changes

* Change lister.go

* Change saver.go

* Change imports

* Remove unnecessary Count query

* Use IndexView for indexing

* Rename ModuleStore fields

* Use map of key:sorting-order for creating the index

* Minor changes

* Use client options to configure mongo client

* Use method chaining

* gofmt changes

* Change imports

* Fix some build errors

* Use new GridFS API

* Fix more build errors

* Add Go Mongo driver to dependency modules

* Use multierror

* Leave download stream open

* Remove mgo error handling

* Copy zip instead of loading all in memory

* Use context.WithTimeout() wherever possible

* Raise KindNotFound when mod@ver isn't found

* NopCloser not needed

* Fix IndexView error

* Fix build errors

* Remove another mgo error usage

* Fix build error

* Changes according to review

* Formatting changes as per gofmt

* Modify gofmt argument to show the expected formatting (diff)

* Handle ErrNoDocument error and error arising from query execution

* Fix kind of returned error

* Minor changes

* Bug fixes

* gofmt related changes

* Minor change

* Use Insecure from MongoConfig, remove Insecure from global Config

* Remove stray print statement

scripts/check_gofmt.sh

@@ -5,4 +5,4 @@
 set -euo pipefail
 
 GO_FILES=$(find . -iname '*.go' -type f | grep -v /vendor/)   # All the .go files, excluding vendor/
-test -z $(gofmt -s -l $GO_FILES | tee /dev/stderr)
+test -z $(gofmt -s -d $GO_FILES | tee /dev/stderr)