debian/rules: extract build_dep.tar.gz first

dh_auto_build runs the default target of the Makefile in the top
directory. Extract the build deps before running it, to avoid
downloading the build dependencies again (which fails in OBS as we build
without network there). Remove the redundant "rebar3 compile" and
"rebare3 escriptize" commands, which are part of the default target in
the Makefile.

debian/rules was copied from osmo_dia2gsup, but there it works as-is
because osmo_dia2gsup has no Makefile (-> dh_auto_build is a no-op).

Change-Id: I2bb0b5f608cd5d9a24c2a367425c524447bd002c
---
M debian/rules
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/debian/rules b/debian/rules
index 89863f8..72a2bb6 100755
--- a/debian/rules
+++ b/debian/rules
@@ -8,10 +8,8 @@
 	dh $@
 
 override_dh_auto_build:
-	dh_auto_build
 	if [ -e build_dep.tar.gz ] ; then tar xzf ./build_dep.tar.gz ; fi
-	rebar3 compile
-	rebar3 escriptize
+	dh_auto_build
 	rebar3 eunit
 
 override_dh_clean:

