Add support for %h and %r escape characters in IdentityFile for SSH.

[mannjani]

See section "IdentityFile" on https://linux.die.net/man/5/ssh_config for details.

IdentityFile
Specifies a file from which the user's RSA or DSA authentication identity is read. The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for protocol version 2. Additionally, any identities represented by the authentication agent will be used for authentication.

The file name may use the tilde syntax to refer to a user's home directory or one of the following escape characters: '%d' (local user's home directory), '%u' (local user name), '%l' (local host name), '%h' (remote host name) or '%r' (remote user name).

It is possible to have multiple identity files specified in configuration files; all these identities will be tried in sequence.

[Eugeny]

Thank you!

[Eugeny]

@all-contributors add @mannjani for code