libevent: Properly declare OpenSSL dependency version bounds (#2888)

* libevent: Properly declare OpenSSL dependency version bounds

* libevent: Handle ~openssl variant correctly

var/spack/repos/builtin/packages/libevent/package.py

@@ -48,9 +48,10 @@ class Libevent(AutotoolsPackage):
     version('2.0.13', 'af786b4b3f790c9d3279792edf7867fc')
     version('2.0.12', '42986228baf95e325778ed328a93e070')
 
+    # Does not build with OpenSSL 1.1.0
     variant('openssl', default=True,
             description="Build with encryption enabled at the libevent level.")
-    depends_on('openssl', when='+openssl')
+    depends_on('openssl @:1.0', when='+openssl')
 
     def configure_args(self):
         spec = self.spec
@@ -58,6 +59,6 @@ def configure_args(self):
         if '+openssl' in spec:
             configure_args.append('--enable-openssl')
         else:
-            configure_args.append('--enable-openssl')
+            configure_args.append('--disable-openssl')
 
         return configure_args