[2.x] require coreutils for RPM (#8712)

**Problem**
Apparently sbt can fail when it doesn't have rm,
which can happen "when building relocatable RPM's and building an OS image in a chroot."

**Solution**
It was suggested that we require coreutils.

build.sbt

@@ -57,6 +57,9 @@ Global / excludeLint += checkPluginCross
 Global / excludeLint += nativeImageJvm
 Global / excludeLint += nativeImageVersion
 
+usePgpKeyHex("642AC823")
+// usePgpKeyHex("2BE67AC00D699E04E840B7FE29967E804D85663F")
+
 def commonSettings: Seq[Setting[?]] = Def.settings(
   headerLicense := Some(
     HeaderLicense.Custom(

launcher-package/build.sbt

@@ -101,7 +101,6 @@ val launcherPackage = (project in file(".")).
         case _ => Nil
       }
     },
-    usePgpKeyHex("642AC823"),
     pgpSecretRing := file(s"""${sys.props("user.home")}""") / ".ssh" / "scalasbt.key",
     pgpPublicRing := file(s"""${sys.props("user.home")}""") / ".ssh" / "scalasbt.pub",
     publishToSettings,
@@ -302,11 +301,11 @@ val launcherPackage = (project in file(".")).
     rpmVendor := "scalacenter",
     rpmUrl := Some("http://github.com/sbt/sbt-launcher-package"),
     rpmLicense := Some("Apache-2.0"),
-    // This is intentionally empty. java-devel could bring in JDK 9-ea on Fedora,
+    // This is intentionally does not list Java. java-devel could bring in JDK 9-ea on Fedora,
     // and java-1.8.0-devel doesn't work on CentOS 6 and 7.
     // https://github.com/sbt/sbt-launcher-package/issues/151
     // https://github.com/elastic/logstash/issues/6275#issuecomment-261359933
-    rpmRequirements := Seq(),
+    rpmRequirements := Seq("coreutils"),
     rpmProvides := Seq("sbt"),
 
     // WINDOWS SPECIFIC