TT#25551 Improve the way to detect installed packages

"dpkg-query -s" doesn't give the desired answer, it includes packages
known to dpkg for different reasons, but does not exactly reply
whether they are installed or not, which is the intention of the code.

Change-Id: I84b4a6c4c7c84997c31b2bdb3f10e0fe9ab0b721

t/api-rest/Dockerfile

@@ -5,7 +5,7 @@ FROM docker.mgm.sipwise.com/sipwise-stretch:latest
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2017-09-21
+ENV REFRESHED_AT 2017-11-22
 
 # files that get-code generates
 COPY t/api-rest/sources.list.d/builddeps.list /etc/apt/sources.list.d/
@@ -34,7 +34,7 @@ RUN dpkg --force-depends -i /tmp/ngcp-panel-tests-rest-api-build-deps_1.0_all.de
 RUN apt-get --assume-yes -f install
 # Ensure package ngcp-panel-tests-rest-api-build-deps is installed as
 # apt-get might just remove it instead of installing (due to force option).
-RUN dpkg-query -s ngcp-panel-tests-rest-api-build-deps
+RUN test "$(dpkg-query -f '${db:Status-Status} ${db:Status-Eflag}' -W ngcp-panel-tests-rest-api-build-deps 2>/dev/null)" = 'installed ok'
 
 # for prove execution
 RUN wget http://deb.sipwise.com/files/libtest-pretty-perl_0.31-1~bpo80+1_all.deb