VMware warm migration - Fix snapshot cleanup

[mnecas]

Issue:
The CreateSnapshot is after RemovePreviousSnapshot so with the warm migration, we always skipped the snapshot cleanup step.

Fix:
Get the next migration phase dynamically. This way the VMware migration will run RemovePreviousSnapshot and the other migrations will run `CreateSnapshot``.

Ref:
https://issues.redhat.com/browse/MTV-1656

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 15.65%. Comparing base (71d4376) to head (10089c4).

Files with missing lines	Patch %	Lines
pkg/controller/plan/migration.go	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1189   +/-   ##
=======================================
  Coverage   15.65%   15.65%           
=======================================
  Files         112      112           
  Lines       23071    23071           
=======================================
  Hits         3612     3612           
  Misses      19174    19174           
  Partials      285      285           

Flag	Coverage Δ
unittests	15.65% <0.00%> (ø)

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[mansam]

LGTM