Fix sshkeys passphrase issue with `mila init` [MT-72]

[lebrice]

• [X] Find a way to reproduce #91
  • I was able to reproduce this on a Windows machine with no prior SSH setup done. Running mila init goes fine until it copies the SSH public key over to the authorized_keys file on the remote. This doesn't seem to work. There are extra ^M characters in the authorized_keys file on the cluster. Doing ssh mila asks for a passphrase (empty) and then asks for a password, then connects successfully.
• [X] Fix the issue
  • I'm not 100% sure I've identified the cause, BUT:
  • I've ran the command from both Windows and Linux machines with no initial SSH configuration, and it works, whereas it didn't before.

Seems like the issue is caused by passing the passphrase using f"-N '{passphrase}'", as in ssh-keygen -t rsa -f {file_path} -N '{passphrase}'. I believe setting f"-N='{passphrase}'" might fix it.

Old command: ssh-keygen -t rsa -f {file_path} -N '{passphrase}' New command: ssh-keygen -t rsa -f {file_path} -N='{passphrase}'

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.42857% with 10 lines in your changes missing coverage. Please review.

Project coverage is 61.03%. Comparing base (f8bb9c1) to head (f938f9c). Report is 18 commits behind head on master.

Files with missing lines	Patch %	Lines
milatools/cli/init_command.py	70.37%	8 Missing :warning:
milatools/cli/local.py	80.00%	1 Missing :warning:
milatools/cli/remote.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #93 +/- ## ========================================== + Coverage 60.91% 61.03% +0.12% ========================================== Files 9 9 Lines 1379 1404 +25 ========================================== + Hits 840 857 +17 - Misses 539 547 +8 ``` | [Flag](https://app.codecov.io/gh/mila-iqia/milatools/pull/93/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | Coverage Δ | | |---|---|---| | [integrationtests](https://app.codecov.io/gh/mila-iqia/milatools/pull/93/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `11.18% <5.71%> (-0.21%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/mila-iqia/milatools/pull/93/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `61.03% <71.42%> (+0.12%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia#carryforward-flags-in-the-pull-request-comment) to find out more.

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