Add trailing slash if needed on SetUrl method

[sverdlov93]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.

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following #707

Also:

1. Remove the leading slash if it exists on the target path to avoid wrong target parsing.
2. Comments have been added to clarify some potentially confusing lines of code.
3. Fix failing terraform update test.