mkarchiso: run _cms_sign_artifact only once

Since `_build_buildmode_netboot` runs `_build_iso_base` which runs
`_prepare_airootfs_image`, the call to `_cms_sign_artifact` in
`_build_buildmode_netboot` can be removed.

Fixes #197

1 files changed, 2 insertions, 0 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 86cdc02..31e48df 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -17,6 +17,8 @@ Deprecated
 Fixed
 -----
 
+- Sign the root file system image only once.
+
 Removed
 -------