Formatter: add a dump_format_ns to base Formatter

`dump_format_ns` is a generic formatter to dump a simple format along
with a namespace. It is `dump_format` with an optional ns. This also
extends the XML formatter with this functionality. This allows creation
of xml tags with ns and a specified format. The JSON Format doesn't
define a ns, and here the functionality is exactly same as that of
`dump_format`

Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@ril.com>
rgw_formats: dump_format_ns implementation

Since the base formatter was extended with a dump_format_ns class,
implementing this here. For now, this is exactly same as dump_format, as
the concept of ns in json is not used.

Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@ril.com>
s3: update get_location based on new formatter

This updates the s3's get bucket location based on the new formatter
which allows xml ns to be embedded.

Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@ril.com>
test/formatter: Add tests for dump_format_ns

Adding basic unit test to test the new formatter class'
dump_format_ns. Since the functionality only affects XML (and other
implementations mimic dump_format exactly), tests are added for these.
`fmt.close_section()` is avoided in the tests as this calls an
assert (and there is no section to close) and this triggers a test
failure.

Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@ril.com>