Fix integration tests

[adriangonz]

Fixes #1076.

Changelog

• Make tensorflow check more robust by testing the presence of what we need to import later on
• Use local version of seldon-core on integration tests

[adriangonz]

/test lint

[adriangonz]

/test lint

[adriangonz]

/test this

[adriangonz]

/ok-to-test

[adriangonz]

/test this

[adriangonz]

/test integration

[axsaucedo]

/test integration

[axsaucedo]

It seems the integration tests is getting stuck on:```Error from server (NotFound): deployments.extensions "mymodel-mymodel-e2eb561" not found
seldondeployment.machinelearning.seldon.io/mymodel created
Waiting for deployment "mymodel-mymodel-e2eb561" rollout to finish: 0 of 1 updated replicas are available...
deployment "mymodel-mymodel-e2eb561" successfully rolled out
seldondeployment.machinelearning.seldon.io/mymodel configured

Retesting again to see if it passes through this. 

/test all

[seldondev]

@adriangonz: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
integration	4dd0696	link	/test integration

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[axsaucedo]

Awesome stuff, this fixes it!
/approve

[axsaucedo]

/lgtm

[seldondev]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: axsaucedo

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [axsaucedo]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment