Allow to pass a NULL 'keys' argument to osinfo_loader_entity()

Some callers don't want to pass in any additional keys, and would have to
resort to build a dummy empty key list to pass to osinfo_loader_entity().
It's better to allow for that 'keys' argument to be NULL and have
osinfo_loader_entity() deal with it.
Add type info to osinfo_loader_entity() 'key' argument

When using 'string(./foo)' as an XPath query, if foo does not exist, an
empty string ("") will be returned. Thus osinfo_loader_string() ignores
empty strings during parsing. This happens during regular parsing as we try
to lookup string(./foo[lang(XX-xx)]) for localized nodes,  and ignore its
result if the XPath query returns ""

However, we want to represent booleans as <foo/>. Boolean values are
currently parsed using osinfo_loader_string(). Parsing <foo/> as a string
would return an empty string. This means such nodes would be ignored as the
current parser is not able to make the difference between an existing node
with empty content and a non-existing node.

By associating type information to the additional keys we want
osinfo_loader_entity() to parse, we'll be able to indicate which values are
booleans, and to parse them accordingly.
Teach osinfo_loader_entity() how to parse booleans

We want to support both <foo>true</foo> and <foo/> to specify booleans. Now
that osinfo_loader_entity additional keys have type information, we can
use a dedicated boolean parser for boolean keys.
Stop using <foo>true</foo> in libosinfo database

libosinfo can now parse <foo/> as an alternative to <foo>true</foo> to
represent a boolean. As the former is the preferred representation, switch
to using this in the data libosinfo ships.
Fix warnings in OsinfoLoader boolean support

I always build with -O0, which sometimes makes me some warnings. The newly
introduced boolean support in OsinfoLoader triggers some warnings when building with the
default flags:

osinfo_loader.c: In function 'osinfo_loader_boolean':
osinfo_loader.c:200:255: error: return makes integer from pointer without a cast [-Werror]
     g_return_val_if_fail(ctxt != NULL, NULL);
                                                                                                                                                                                                                                                               ^
osinfo_loader.c:201:257: error: return makes integer from pointer without a cast [-Werror]
     g_return_val_if_fail(xpath != NULL, NULL);
                                                                                                                                                                                                                                                                 ^
osinfo_loader.c: In function 'osinfo_loader_entity.isra.8':
osinfo_loader.c:331:48: error: 'value_bool' may be used uninitialized in this function [-Werror=maybe-uninitialized]
                 osinfo_entity_set_param_boolean(entity, keys[i].name, value_bool);
debian: add installer script

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
ubuntu: Add jeos install-script (version >= 6.06)

script base on: https://github.com/clalancette/oz/tree/master/oz/auto

gscrivan: add ubuntu 13.04