Fix/Grant update failed: not allowed to create a user with grant

[alereca]

Description of your changes

Fixes #127

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.

How has this code been tested

• Manually, by creating grants for users with host=localhost and then checking if the resource reconciliation was successful.
  • Also checked in dbs whether grants were applied
• Wondering if I should update ./cluster/local/integration_tests.sh to test this scenario, since unit tests do not seem to be a good fit for this

[Duologic]

A rebase should re-trigger CI.

sorry for the late responses to your PRs, I had other priorities

[alereca]

A rebase should re-trigger CI.

sorry for the late responses to your PRs, I had other priorities

No problem, thanks for reviewing them!

I've just merged master to fix the conflicts if you would like to check it and merge it later.

I forgot to sign-off so I had to perform a force push, consequently all checks got blocked again