Add scheme param to import_rsa_publickey_from_file

[danixeee]

Description of the changes being introduced by the pull request:

Allow passing scheme argument when importing RSA public key from file.

Please verify and check that the pull request fulfills the following
requirements:

• The code follows the Code Style Guidelines
• Tests have been added for the bug fix or new feature
• Docs have been added for the bug fix or new feature

[coveralls]

Coverage remained the same at 100.0% when pulling bfa5f03 on openlawlibrary:danixeee/load-rsa-keys-with-scheme into d6227b4 on secure-systems-lab:master.

[lukpueh]

LGTM, thanks!