I had the same problem, this troubleshot helped me getting close to the solution:
Summing up, what i did, i don't know if all these steps are necessary, so you should test after each one:
1) In SQL Server configuration manager enable Named Pipes in protocols
2) In the VM add a windows firewall inbound rule for sql server port (in my case the default 1433, in yours it seems to be 1435, make sure it's 1435 in sql server configuration)
3) Make Sure you are using a sql server authentication login (not a windows authentication) if you don't have one create it locally in the VM>MSSMS
4) Make Sure the SQL server is configured for mixed authentication (http://www.katieandemil.com/microsoft-sql-server-error-18456-login-failed-for-user)
5) Make sure sql server browser is running
Hope this helps :)