allow @ symbol in user for ssh connections (#129)

* allow @ symbol in user for ssh connections

Previously, the @ symbol was only used as a way to either:
- separate the user from the host
- separate "sudo" from the user

This change expands this to allow the username part of
sudo@username@host or username@host to contain any number of @ symbols
in addition to the ones previously allowed. Host is not allowed to
contain an @ symbol as per the usual definition.

* clean up regex changes

Moved the dash in the regex pattern to the end to make it explicitly
clear that it isn't part of a range.

Removed the hostNameRe regex as it is unused.

wavesrv/pkg/cmdrunner/cmdrunner.go

@@ -103,8 +103,7 @@ var SetVarScopes = []SetVarScope{
 	{ScopeName: "remote", VarNames: []string{}},
 }
 
-var hostNameRe = regexp.MustCompile("^[a-z][a-z0-9.-]*$")
-var userHostRe = regexp.MustCompile("^(sudo@)?([a-z][a-z0-9._-]*)@([a-z0-9][a-z0-9.-]*)(?::([0-9]+))?$")
+var userHostRe = regexp.MustCompile("^(sudo@)?([a-z][a-z0-9._@-]*)@([a-z0-9][a-z0-9.-]*)(?::([0-9]+))?$")
 var remoteAliasRe = regexp.MustCompile("^[a-zA-Z][a-zA-Z0-9_-]*$")
 var genericNameRe = regexp.MustCompile("^[a-zA-Z][a-zA-Z0-9_ .()<>,/\"'\\[\\]{}=+$@!*-]*$")
 var rendererRe = regexp.MustCompile("^[a-zA-Z][a-zA-Z0-9_.:-]*$")