MDEV-23589: Portability: use `uname -n` instead of `hostname`

Closes PR #1663

scripts/CMakeLists.txt

@@ -162,7 +162,7 @@ ELSE()
   SET(CHECK_PID "kill -s SIGCONT $PID  > /dev/null 2> /dev/null")
 ENDIF()
 
-SET(HOSTNAME "hostname")
+SET(HOSTNAME "uname -n")
 SET(MYSQLD_USER "mysql")
 ENDIF(UNIX)
 

support-files/CMakeLists.txt

@@ -30,7 +30,7 @@ ELSE()
   SET(CXXFLAGS ${CMAKE_CXX_FLAGS})
   SET(MYSQLD_USER "mysql")
   SET(ini_file_extension "cnf")
-  SET(HOSTNAME "hostname")
+  SET(HOSTNAME "uname -n")
 ENDIF()
 
 # XXX: shouldn't we just have variables for all this stuff and centralise