How can one get host IP address from within vbox virtual machine? I'm trying to clone repository running on the host, so I need an address to perform
That all depends on your networking arrangement.
If you are using a NAT or Host Only arrangement then the hosts's IP address will be your default route provided by DHCP by the host.
If you are bridging your network then there is no way to automatically know the host's IP address.
This doesn't answer the question, but perhaps solves the problem.
To clone a hg repository, I would uses shared folders in this case. HOWTO: Use Shared Folders