Add user diag, add root password, add debug tweaks

Struggling with petalinux update: it is no longer possible to log as
root without the tweaks.

From user diag, it is possible to sudo.

recipes-core/images/zup-image-soleil-fofb.bb

@@ -17,6 +17,7 @@ require ./recipes-core/images/techlab-common.inc
 IMAGE_FEATURES_append = " \
     package-management \
     petalinux-python-modules \
+    debug-tweaks \
     "
 
 # If we want FPGA manager
@@ -43,3 +44,10 @@ IMAGE_FEATURES_remove = " x11 wayland opengl qt jupyter"
 # Remove unwanted features
 DISTRO_FEATURES_remove = " wifi bluetooth 3g nfc"
 
+# User
+inherit extrausers
+EXTRA_USERS_PARAMS = "\
+    usermod -s /bin/zsh -P 'fofb' root; \
+    useradd -s /bin/zsh -G sudo -P 'diag91' diag; \
+    "
+