core/pkg-generic: check proper package installation

core/pkg-generic: check proper package installation

Some packages misbehave, and install files in either $(STAGING_DIR)/$(O)
or in $(TARGET_DIR)/$(O) .

One common reason for that is that pkgconf now prepends the sysroot path
to all the paths it returns. Other reasons vary, but are mostly due to
poorly writen generic-packages.

And a new step hooks to check that no file gets installed in either
location, called after the install-target and install-staging steps.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>