Workflows and volumes enhancements

[filippomc]

Closes #505
Closes #506
Closes #512

Implemented solution

#506: Readonly volumes can be added with the :ro at the end of the shared_directory string.
#505: Multiple values are allowed for pod_context as list or tuple

cloud-harness/libraries/cloudharness-common/tests/test_workflow.py

Line 236 in 6bb7a96

pod_context=(

#512 pod contexts are added automatically for volumes specified as shared_directory

How to test this PR:
Unit tests are covering the functionality.

Create an operation like

op = operations.ParallelOperation('test-parallel-op-', (tasks.PythonTask('p1', f), tasks.PythonTask('p2', f)),
                                      pod_context=(
                                        operations.PodExecutionContext('a', 'b'), 
                                        operations.PodExecutionContext('c', 'd', required=True), 
                                        operations.PodExecutionContext('e', 'f')
                                        )), shared_directory = 'myclaim:/mnt/shared:ro'

and see that the workflow specification has 4 affinity terms 2 required, 2 preferred and a readonly mounted volume

Sanity checks:

• The pull request is explicitly linked to the relevant issue(s)
• The issue is well described: clearly states the problem and the general proposed solution(s)
• From the issue and the current PR it is explicitly stated how to test the current change
• The labels in the issue set the scope and the type of issue (bug, feature, etc.)
• All the automated test checks are passing
• All the linked issues are included in one milestone
• All the linked issues are in the Review/QA column of the board
• All the linked issues are assigned

Breaking changes (select one):

• The present changes do not change the preexisting api in any way
• This PR and the issue are tagged as a breaking-change

Possible deployment updates issues (select one):

• There is no reason why deployments based on CloudHarness may break after the current update
• This PR and the issue are tagged as alert:deployment

Test coverage (select one):

• Tests for the relevant cases are included in this pr
• The changes included in this pr are out of the current test coverage scope

Documentation (select one):

• The documentation has been updated to match the current changes
• The changes included in this PR are out of the current documentation scope

Nice to have (if relevant):

• Screenshots of the changes
• Explanatory video/animated gif

[zsinnema]

nice!
lgtm