Fully-qualify Msf::DBImportError

MSP-11152

Constant was unqualified in some of the reorganized Msf::DBManager code
because that code was take advantage of the old nested lexical scope
that included `Msf`.
Use :: to force top-level constant resolution

MSP-11152

When `Msf::DBManager::Import::MetasploitFramework` is included in
`Msf::DBManager::Import`, it's child namespace of
`Msf::DBManager::Import::MetasploitFramework::Zip becomes resolvable as
`Zip` in `Msf::DBManager::Import` methods, so need to use `::Zip` to
cause `Zip` to be resolved from rubyzip gem.
Fully-qualify Msf::ServiceState

MSP-11152

Replace unqualified `ServiceState` with `Msf::ServiceState`.
Merge branch 'landing/4042' into upstream-master

Land #4042

 the commit.