Disallow dot and hyphen as first character of hostnames

- Causes hostname to be set to an invalid value on some systems which
  also causes malfunction of hostname -f so it cannot be changed

plugins/kernel_v2/config/vm.rb

@@ -353,7 +353,7 @@ module VagrantPlugins
         errors << I18n.t("vagrant.config.vm.box_not_found", :name => box) if \
           box && !box_url && !machine.box
         errors << I18n.t("vagrant.config.vm.hostname_invalid_characters") if \
-          @hostname && @hostname !~ /^[-.a-z0-9]+$/i
+          @hostname && @hostname !~ /^[a-z0-9][-.a-z0-9]+$/i
 
         has_nfs = false
         used_guest_paths = Set.new

templates/locales/en.yml

@@ -691,7 +691,7 @@ en:
         box_not_found: "The box '%{name}' could not be found."
         hostname_invalid_characters: |-
           The hostname set for the VM should only contain letters, numbers,
-          and hyphens.
+          hyphens or dots. It cannot start with a hyphen or dot.
         network_invalid: |-
           The network type '%{type}' is not valid. Please use
           'hostonly' or 'bridged'.