Send post login string as SSH command when no shell session is requested.

[s3lph]

There is currently no way for ConnectBot to send a command to a SSH server without allocating a PTY. The "post login string" is only ever sent if a PTY is requested and allocated, and then it is simply sent as an input to the PTY. Issue #1128 describes a similar, if not identical issue.

This is especially limiting if a remote SSH server only permits executing commands. Probably the most common example is OpenSSHd's ForceCommand option: It requires any command (or a shell) to be started before ForceCommand takes effect. ConnectBot, however, won't start a shell unless PTY allocation succeeds.

This PR adds the following feature: If establishing a session is disabled, but a post login string is provided, the post login string is executed as a command through SSH, rather than being piped into a shell. The local and telnet transports implement post login string handling in this scenario as well, but they simply forward it to their write method in the same way the TransportBridge.injectString method already does.

[CLAassistant]

All committers have signed the CLA.