vyatta-cfg-dhcp-server: formatting changes for style consistency

Update scripts/system/dhcpd-config.pl to have consistent identation
levels and style throughout.
vyatta-cfg-dhcp-server: formatting changes for style consistency

Update scripts/system/dhcpdv6-config.pl to have consistent identation
levels and style throughout.
vyatta-cfg-dhcp-server: formatting changes for style consistency

Tidy up use statements and initial variable declarations in
scripts/system/dhcpd-config.pl
vyatta-cfg-dhcp-server: don't prefix hostname with use-host-decl-names

The fix for Bug #160 causes issues when the hostname provided by the
DHCP server is expected to be exactly as given when using the option
"use-host-decl-names" (eg for PXE booting), this is one of the options
that aren't validated by the CLI.  This fix disables adding the prefix
to the hostname when this option is passed, and although this could
result in a broken config, the user is already prompted that this could
happen when it is set and to check the logs to confirm correct
operation of DHCP afterwards.

Bug #334 http://bugzilla.vyos.net/show_bug.cgi?id=334