TT#17961 Install dirmngr on Debian Stretch for 'apt-key adv --recv-keys'

Otherwise:
>> apt-key adv --recv-keys --keyserver pool.sks-keyservers.net 6F6B15509CF8E59E6E469F327F438280EF8D349F
> Executing: /tmp/apt-key-gpghome.Enz9Bpg23h/gpg.1.sh --recv-keys --keyserver pool.sks-keyservers.net 6F6B15509CF8E59E6E469F327F438280EF8D349F
> gpg: failed to start the dirmngr '/usr/bin/dirmngr': No such file or directory
> gpg: connecting dirmngr at '/tmp/apt-key-gpghome.Enz9Bpg23h/S.dirmngr' failed: No such file or directory
> gpg: keyserver receive failed: No dirmngr

It looks like 'dirmngr' should be an dependency for the package 'apt'
in Debian Stretch, while it is not there.

Change-Id: I8753caddcccfc8e3287936c92706ba5e2148d31d

deployment.sh

@@ -2331,6 +2331,11 @@ EOF
 
   chroot $TARGET apt-get -y install resolvconf libnss-myhostname
 
+  if [ "$DEBIAN_RELEASE" = "stretch" ] && [ ! -x "${TARGET}/usr/bin/dirmngr" ] ; then
+    echo  "Installing dirmngr on Debian Stretch otherwise 'apt-key adv --recv-keys' is failing to fetch GPG key"
+    chroot $TARGET apt-get -y install dirmngr
+  fi
+
   echo "Installing 'puppet-agent' with dependencies"
 
   # puppetlabs hasn't provided packages for Debian Stretch yet