tests/docker: Added libbpf library to the docker files.

The series of patches for eBPF RSS adds libbpf dependency for qemu.
https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg08887.html

With this patch, libbpf added:
  Alpine - added libbpf-dev
  Centos 8 - added libbpf-devel
  Fedora - added libbpf-devel

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210406082947.672708-2-andrew@daynix.com>
Message-Id: <20210512102051.12134-11-alex.bennee@linaro.org>

tests/docker/dockerfiles/alpine.docker

@@ -20,6 +20,7 @@ ENV PACKAGES \
 	gnutls-dev \
 	gtk+3.0-dev \
 	libaio-dev \
+	libbpf-dev \
 	libcap-ng-dev \
 	libjpeg-turbo-dev \
 	libnfs-dev \

tests/docker/dockerfiles/centos8.docker

@@ -14,6 +14,7 @@ ENV PACKAGES \
     git \
     glib2-devel \
     libaio-devel \
+    libbpf-devel \
     libepoxy-devel \
     libfdt-devel \
     libgcrypt-devel \

tests/docker/dockerfiles/fedora.docker

@@ -32,6 +32,7 @@ ENV PACKAGES \
     libcurl-devel \
     libepoxy-devel \
     libfdt-devel \
+    libbpf-devel \
     libiscsi-devel \
     libjpeg-devel \
     libpmem-devel \