Replace python-nose with unittest

= changelog =
resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1916782

dnf-plugins-core.spec

@@ -100,10 +100,8 @@ Summary:        Core Plugins for DNF
 BuildRequires:  python2-dnf >= %{dnf_lowest_compatible}
 %if 0%{?rhel} && 0%{?rhel} <= 7
 BuildRequires:  dbus-python
-BuildRequires:  python-nose
 %else
 BuildRequires:  python2-dbus
-BuildRequires:  python2-nose
 %endif
 BuildRequires:  python2-devel
 %if 0%{?fedora}
@@ -147,7 +145,6 @@ Summary:    Core Plugins for DNF
 BuildRequires:  python3-dbus
 BuildRequires:  python3-devel
 BuildRequires:  python3-dnf >= %{dnf_lowest_compatible}
-BuildRequires:  python3-nose
 %if 0%{?fedora}
 Requires:       python3-distro
 %endif

tests/CMakeLists.txt

@@ -1,4 +1,4 @@
-ADD_TEST(test ${PYTHON_EXECUTABLE} -m nose -s ${CMAKE_CURRENT_SOURCE_DIR})
+ADD_TEST(test ${PYTHON_EXECUTABLE} -m unittest discover -t ${CMAKE_CURRENT_SOURCE_DIR}/.. -s ${CMAKE_CURRENT_SOURCE_DIR})
 
 # ASAN_OPTIONS is for libdnf built with sanitizers, has no effect otherwise.
 SET_PROPERTY(TEST test PROPERTY ENVIRONMENT "PYTHONPATH=${CMAKE_SOURCE_DIR}/plugins;ASAN_OPTIONS=verify_asan_link_order=0")

tests/README

@@ -2,7 +2,5 @@ To run tests from the source tree, run this
 (working directory = root of the source tree):
 
 export PYTHONPATH=./plugins
-nosetests tests/
+python3 -m unittest discover -t . -s tests/
 
-You can run tests under specific Python version using nosetests-2.7
-or nosetests-3.4.