Do not intern empty strings

The nimsoft configuration can contain settings with no value, e.g.

    suspended =

where we'd normally expect a value of `yes` or `no`. If we instruct the
provider to intern such a value we fail on ruby < 1.9 because an empty
string has no symbol representation.

Symbols as property values should only be used if there is a limited set
of allowed values that this property can have (e.g. `yes` and `no`). In
that case an empty value does not make sense and should be treated as if
the corresponding property was absent.

Result: If the manifest author does define a resource with a property
set to a specific value and this value is empty in the current
configuration, puppet will explicitly set it.
Add more properties to nimsoft_oracle_profile

Puppet can now change every attribute of an oracle profile. This can be
vital because the probe seems to sent invalid messages if some
attributes have not been set explicitly (the probe seems to lack certain
default values), which previously could not be set through puppet (e.g.
timeout message or severity of timeout messages)