fix ARM64 docker image build (#1370)
fix ARM64 docker image build (#1370)

For building VPP was used gcc-7 which ended by failure on ARM64 platform
gcc-8 and g++-8 are installed and used instead to ensure successfull build
VPP is built with gcc-8 for both platform variants - x86_64 and aarch64 successfully

Signed-off-by: Stanislav Chlebec <c0cbfd1f0d33178bb911156d16e6e62b9136364d@pantheon.tech>
ondrej-fabry/vpp-agent,ondrej-fabry/vpp-agent,VladoLavor/vpp-agent,VladoLavor/vpp-agent,ondrej-fabry/vpp-agent,VladoLavor/vpp-agent