sap_vm_provision: Add variable validations

[marcelmamula]

Changes

• Add dedicated tasks for validation of variable for each supported combination.
  • Validate if variable is defined, correct type and not empty
  • Separation of validation for extra variables that are required only for ansible.
• Add validation for variables that are used as keys in dictionaries. (Solves sap_vm_provision: Add fail task when image was not found #79)

Tested

Tested on AWS using ansible-core 2.18 and 2.19

[ja9fuchs]

good check 👍