Don't exit on eof in header reading in stdcopy

There was random lines drops in docker logs because of this
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Convert TestGetContainersByName into a unit test

Docker-DCO-1.1-Signed-off-by: Guilherme Salgado <gsalgado@gmail.com> (github: gsalgado)
Move TestBuildEntrypointRunCleanup to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestForbiddenContextPath to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildADDFileNotFound to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildInheritance to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildFails to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildFailsDockerfileEmpty to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildOnBuildTrigger to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildOnBuildForbiddenChainedTrigger to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildOnBuildForbiddenFromTrigger to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildOnBuildForbiddenMaintainerTrigger to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Move TestBuildAddToSymlinkDest to integration-cli

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Update libcontainer dependency to 77ffd49dfedbc78a

Fixes #6256
Fixes #6383
Fixes #6414

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
prevent panic when empty flag

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #6471 from LK4D4/more_buildfile_tests_to_cli

Move more buildfile tests to integration-cli
Merge pull request #6485 from crosbymichael/update-libcontainer

Update libcontainer dependency to 77ffd49dfedbc78a
Merge pull request #6405 from gsalgado/migrate-test-getcontainersbyname

Convert TestGetContainersByName into a unit test
Merge pull request #6489 from vieux/fix_mflags_panic

prevent panic when empty flag
Merge pull request #6320 from LK4D4/fix_stdcopy_eof

Don't exit on eof in header reading in stdcopy